Hydraulic system comprising a servomotor of the follow-valve type and improved control means therefor



Jan. 1, 1952 M, MAY

HYDRAULIC SYSTEM COMPRISING A SERVOMOTOR OF THE FOLLOW-VALVE TYPE AND IMPROVED CONTROL MEANS THEREFOR 4 Sheets-Sheet 1 Filed Dec. 3. 1949 Gttorneg Jan. 1, 1952 2,580,686

E. M. MAY HYDRAULIC SYSTEM COMPRISING A SERVOMOTOR OF THE FOLLOW-VALVE TYPE AND IMPROVED CONTROL MEANS THEREFOR Filed Dec.

4 Sheets-Sheet 2 Imoemor Gttomeg Jan. 1, 1952 MAY HYDRAULIC SYSTEM COMPRISING A SERVOMOTOR OF THE FOLLOW-VALVE TYPE AND IMPROVED CONTROL MEANS THEREFOR 4 Sheets-Sheet 3 Filed Dec. 5. 1949 OX OQ I :nwemor Jan. 1, 1952 E M MAY 2,580,686

HYDRAULIC SYSTEM-COMPRISING A SERVOMOTOR OF THE FOLLOW-VALVE TYPE AND IMPROVED CONTROL MEANS THEREFOR Filed Dec. 5. 1949 4 Sheets-Sheet Z'mventor Patented Jan. 1, 19 52 VOMQTOR E "THE EOLLOW YALYE i TIRE; AN D: IMPROVED CONTRQL'MEANS THERE- sawaramemy; Detroit, Mich;assienor -to' lvlcd Pilot Manufacturing companyzf'nen oitg: Miami a 'ccr porationiof Michigam Apsuc'suaan cemuer s, laillifsriallvolEH52?" This" invention relates to" improvements in hydraulic" drive and control. systems of a? type in which a movable machine element is moved: and controll'edby a hydraulic motorhaving a followvalve for control of the admissioniand' exhaust of the. motor workihgffluid'andin" which the follow-valve iof the motor actuated by..a hy-. draulic transmitter andboritinuoiislil controlled in its position bythe position of the transmitter piston or plunger.

A hydraulic system of the character specified is shown in my copending application Serial No; 719,305ffi11edll3'ehembr 36, l94'filnow abandoned, which may be. referred1to; for a detaileddisclosure. The apparatus as there disclosedis em ployed to drive respective elements of a turret lathe and thehyd'rauliclpartsdith system comprise a plurality of reciprocating,motors'ofthe follow-valve typeeachIoperatively connected to a. lathe e1ement,jmeans for supplyingapnessure fluid to the motors, and means for actuating the follow-valve of e'achmotor comprising a piston connectedhto the valve element. andl'exposed to hydraulicwpressure in a receiver chamber-,; a. piuralityof-hydraulictransmitters ot tvhich each has its fiuidl chamber connected..,by conduitfto" the receiver chambersofrone of-the.-follow-Valves; and actuatingcams forthe transmitters mounted on. a rotatablysupported-mctor-drivencylihden or carrier." In the operation of such; a-syst'em the hydraulic motor pistons are subject tov the continuous positional controlof 1 the transmitter pistons andtheir positions inturn aredetermined bythe form.ofetheir-iactuatingcams. I

It is an object of the presentv invention to. provide; ahydraulic system. of thetype above described in which themovementsotthe machine element-1 determined by-u'the "follow-valve are caused to conformto predetermined dimensions more accurately than can be obtained from the hydraulic transmitter alone. I

It is also an object of the invention to provide a hydraulicsystem .of the. specified type inwhich the follow-valve movements canbe made to -de part, in a predetermined mannenirom the oontrol of the transmitter in accordance with operating. conditions afiecting the follow-valve; motor. of the elementvdriven by. it.

Additional objects of. the invention n oreor less ancillary, incidental-or supplemental to those stated above will be apparent from the disclosure whichv follows.

In v accordance. with thel invention the i stated objects; and others "ancillary or incidental to thosetreferred'i toab ore. ,aretattained.-fiy;providirig so onz'tli'e supplementary means serving'byposicomma: (01. 121-45) inas's'oeiationwitHthe follbw valve andits motor mechanical" means -which cooprate withthefollow va-lve'tosupplementthe'control thereof'by the: transmitter- -a predetermined 1 manner; Such supplementary control means may takefa varietyorrdrms such; for example as'-" a template device of one form-or another; stop devices? and awe-engagement with the follow valvw or part connecte'd thereto; toaetermme thposition of the movable element of we follow-waive m'o'tor with "a 'hi'gh degree of accuracy? By way of further explanation' of-the invention and ways in-'vvhich it-can be pr'ac'ticed reference ls ha'd "to the" accompanying drawings showine exemplary embodiments and tame detailed de scriptio'n thereof which "follows", the nature and scope of-the invention being particularly-pointed out the appended claims.

manedrawiiigs, Fig. 1 is a plan view, largely diagrammatic; showihg'a portionof aturning lathe and hydraulic" apparatus embodying the' invention: and arranged to drive and control the cuttingt'oolof the lathe. a n

Figi 2"is-alverticalsectiohalview of'a drilling or tapping ffi par'atus having hydraulic driving? and controlling? apparatus presenting another embed iment off'thinventionfsome features" of the hydraulic? apparatus being shown dia'grainrria- Fig: 3is a ve'rticalsectional view of a'drilling' or "tapping apparatus of the type shown in Fig" 2 but 'having'a modified form of control mea'ns.

Fig; 4is a transverse'se'ctionon the line 4"4 of "Fig:"2"slioWing main parts of "th'eapparatus in rear elevation! I Fig: 5 isfa transverse sectionion the rms 5f-5' of Fig'f3 showing some partspf theapparatus' in rear elevation;

Referringfin detail to" the constructions" shown inthedi'awingsahd first'jt'o that shown Fig. '1, numeral I desig ates the main" frame of a turn.- ingrlathe which supports "live" spindle 2; carrying work-holding Ichu'c'k" ayi and the usual-tail stock 41 A carri'ag'e 5, slidablymountedon the fraina ln-tllfii cairies'a .drfiss- 'slide' Bio 11 which is mounted a conventional "compoundilide 6a" carrying' 'a cutting itool 'i"arranged to engagethe work iece WT Compound" slide'fia" aligned parallel to cross slide. 6 for'manualadjiisthient of tool T to cuta workpiece-to desired diameter. 7 r

The carri'age'iS is move'd bya hydraulic motor; designated generally 'bythe numeral 8, .Zwh'ich is rifi-idlybolted?totlielcarriageI Motor 8 is of the follow-valve type and comprises a cylinder 9 in which is mounted piston I having its rod anchored as shown to the frame structure. Motor 8 is controlled by follow-valve |2 of conventional type. The valve is biased towards the right by spring I3 and is fitted at its right end with a piston |4 exposed to the pressure in a hydraulic receiver chamber |5. A follow-rod |6 rigidly connected to piston rod extends into receiver.v chamber l to function in well known manner as a movable displacement plunger or element. Motor 8 is supplied with pressure fluid under control of valve l2 by means of conduit H which may be connected to a suitable source such as. a motor driven pump (not shown), and exhaust. conduits I8 and I9 lead from the valve chamber to exhaust, which may be the sump of the supply pump.

4 and have their cam surfaces formed on the left longitudinal edges of the strips, as shown in the drawing. The cam strips are formed of suitable metal, such as aluminum, and are sufficiently flexible to be bent into circular form and secured, as by screws (not shown) on the surface of a cylinder 50 that may be understood 'to be rotatably mounted on the supporting frame The valve I2 is fitted with a stop rod at was."

extends through the end of the valve casingand is arranged to cooperate, in a manner which,will later be explained, with one or the other of the; stops 2| and 22 which are supported by trough; shaped bracket 23 from mainframe I.

The cross-slide 6 is actuated by means of a hydraulic motor 24 which, except for dimensional differences, is of the same construction as motor 8. The power elements of motor 24 are cylinder body 25, which is rigidly bolted to the cross-slide,

and piston 26 which has its rod 21 anchored to the carriage 5. The follow-valve 28 is biased by spring 29 and is fittedwith piston 30 which 15 open tothe pressure of hydraulic receiver chamber 3| into which extends follow-rod 32 which is rigidly supported from piston rod 21. Conduit 33, which may be connected to the same pump which supplies conduit n, affords a source of working fluid under pressure and exhaust passages 34, 35 may lead to the sump of the same pump. 7

Valve 28 is fitted with a stop rod 36 which is arranged to cooperate with a template 31 mounted on a rigid frame 38 secured by bolts 39, 39'to main frame I'.'

The hydraulic motors 8 and 24 arecontrolled primarily by hydraulic transmitter mechanism which is generally designated by numeral 4|) and is of the same type as that disclosed in my previously mentioned application Serial No. 719,305. While the transmitter mechanism may be embodied as a part of a lathe or other machine tool, it will be assumed that it constitutes a separate unit, as in the case of the construction shown in application Serial No. 719,305.

The transmitter mechanism comprises two hydraulic transmitters generally designated 4| and 42. These transmitters and other parts of the transmitter mechanism will be understood to have suitable support, which may be afforded by a unitary frame structure. mitters 4| and 42 comprises a hydraulic cylinder part 43 in which is mounted a piston or plunger 44 that is biased by spring 45 toward the right. Each cylinder 43 communicates with a gravity feed replenishment reservoir (not shown) through aperture shown by dotted lines at 43a. The cylinder of transmitter 4| communicates through a conduit 46 with the receiver chamber |5 associated with the motor 8 of the lathe, while the cylinder of transmitter 42 communicates through conduit 41 with the receiver chamber 3| associated with motor 24.

The pistons 44 of the transmitters 4| and 42 are actuated by cams 48 and 49, respectively, These cams are in the form of sheet metal strips Each of the transof the transmitter mechanism and driven by an electric. motor (not shown). In the drawing the two cam strips are shown in developed form to facilitate explanation of their construction and operation. v

To effect the movements of the transmitter pistons 44 against the tension of springs 45 cam followers are provided in the form of lever arms 5|; 52. These arms carry anti-friction rollers 53 to engage the active surfaces of the cams and are pivotally mounted on the heads of bolts 54, 54 slidably mounted in the blocks of cylinders 43. Bolts 54 are biased towards the left by coil springs 55 which normally hold the heads of'the bolts yieldingly in contact with the adjacent surfaces of the cylinder blocks. Arms 5|, '52 operatively engage the rods or stems of pistons 44 so that movement of the arms toward the left advances pistons 44 against the tension of springs 45.

An end-wise-slidable'and spring-biased rod 56 is mounted adjacentthe transmitters and carries contact fingers 51 in position to be engaged by the heads of bolts 54 if the bolts are moved towards the right against the tension of springs 55. An electric switch 58 in a circuit that supplies current to the motor that rotates the cylinder 58 is arranged adjacent the end of rod 56 so that movement of the rod toward the right will actuate the switch to open the said circuit.

From the foregoing description it will be apparent that motor 24 and its various adjuncts, other than stop rod 35 and the associated transmitter 42, constitute essentially a conventional follow-valve motor designed for hydraulic transmitter-receiver actuation of the valve; and a corresponding statement is applicable to motor 8 and its adjuncts other than stop rod 28 and transmitter 4|. Thus in the case of motor 24, for example, the automatic follow-valve action is due to follow-rod 32. Assuming the position of cross-slide 6 is such that stop rod 35 is not in contact with template 31 and valve 28 is free to slide in its b'ore, when movement of transmitter piston 44 forces liquid into receiver chamber 3| the pressure on valve piston 30 moves valve 28 upward (on the sheet) to admit working fluid to cylinder 25 above fixed piston 26 so that the cylinder is moved upward relative to the piston, carrying with it the cross-slide 6 and tool 1. This causes a similar movement of receiver chamber 3| relative to fixed follow-rod 32 and enlarges the capacity of the chamber. Aslong as the transmitter piston movement continues to supply liquid to receiver chamber 3| equal in amount to the enlargement of the chamber, valve 23 remains in open position and the motor movement continues. But when transmitter piston 24 stops, the spring-biased valve 28 moves to closed (neutral) position and the motor movement stops. The amounts of the motor and transmitter linear movements are different but proportional, in the ratio of the cross-sectional area of the transmitter piston to that of the follow-rod. The displacement effect of the follow-rod, varying directly with the motor movement,' is the essential function of the said ime. H wever! it m and-Ewe. ad via s tah el fi ivalve structuye, angl actuate thelyalve vin a manvener vto terminate the return rniivefne'nthfthe ratus are shown inthe; positions pcc'up'ied in e med a e of s h el -p pera ib -1ng with the 1'oughed outyvorkp i eee in the lathe, thea triage. ..W1th-va vest0p r0$ 5 t t u ytempla sandi aimt yli der, l pp ie 49. of the 'transm itte1 ;nechanisn1 the tein- I plate- 31 of the iathehaving been designed fbr this purp s n' e .,theP h QU BYFE E the upper ends of the cams en agingtheh c'iflei's to the left to exert pressure fceiv'e'r chamber" 31 of motor 24 and advance stoning 361tgithe right corner of template fl, However, Cam's!) is madea slight amounthigher than is neid to just cause co ntact of stop md SfifW ith the template. This excess height at the cam is marked S on the drawing The excess height of the cam cansescompressiqn oflsprinig jfiiby an amount marked "-T- and putsfa coprespondplate, so that positivevengagernent between the valve structure and template is insgredfndtwithstanding inaccuracies the hygiranlic transmittex' receiver. system. Theeice ss height :ifS 3:.

f t a s m deas na ly son entev ih form v needeqtQeenerate the; mplate shape so thatthe spring oomp ression Ti; staysggnstant and the transmitter rece iver syste m pressure st ys constant Th s cont butes 9 th q y' of the appar s nce yanat n qfd, h n a --pre sure on the. mp ate. tw l-pau ma r al ,;partu1 e from the true positioning of-the-followvalve which is sought. L b

I Be in i g at -1.ine;; ;ca "z4 s er s piisehan v-.-.-feed t e c r a e ,5 .toethet s tt. Mable s p-s 36 owifol owst mpl tefli;ove he d u eml y .zfo moand ca es t ol ith. it. 1 tqd ,s4 al1si w w ile cam A8 qon im s t fee zarr age p at l f oi i i valve .QQntaQ re 2i) strokes stopZl; to position thecai ria ejexactly in line with thes lot in ternplate 3! Cam 48 v rises more thanenoughto ccntactstop} [by the i amount. fUe; which tensions ,the. hydraulicwsystem 20f transmitter-4| Tin themalnner previously de- '3 scribed. .e i Beginning atline C, ca1'n 49 'fe'eds the tool 1 between taWestofif' d1 '20 4 (listen 2 At this to ing tensionon the hydrai i lic transmitt ez 'ece'iter system somewhat in excess cf that necessa -y to nove. the follow v aive into contact Withthe temi tnechanism suitable 'n'eutrai 1 position instead (if b iis' 'ilfitiolvd as wheie y is operated repeatedly to stop mov"' I'fient. 'Fiiitheimorthe anew-valv s respond nstantly when their transmitters are sealed (by the passing of' aprtiii'es 43a) on'their'nextf or- Ward strokes because the? valves are alreadybat revefsapdsition. This sa v motorin thesame direction, thef disciioancy fbewi h Tees F the type in which? a"; p ln'r aiity of table a'refsyiptthieff is see stopping, as follows.

'screw 6! serves to secure body 66 in adjusted position on the base.

Body 56 is formed with a cylinder bore 68 to receive piston 69 carried by tubular rod I which projects from the inner and outer ends of the cylinder bore. Body 66 is also formed with bore ll to receive follow-valve I2 which cooperates with an inlet port T3 and exhaust ports I4 and 15 to control flow of the working fluid to and from cylinder bore 68 through ducts I6 and 11. Valve 12 is biased toward the right by spring I8 and is fitted with a piston I9 which is exposed to the pressure in bore 'II a portion of which serves as a receiver chamber 80. The latter chamber communicates through a conduit ill with a hydraulic transmitter generally designated by 82 and comprising a cylinder element 83 and piston 84. A cam diagrammatically indicated at 85 is of the same type as that disclosed in Fig. 1 and may be considered to be similarly mounted and actuated. This cam actuates piston 84 through a follower arm 86 pivoted to the end of bolt 8? which is slidably supported subject to the pressure of spring 88. The piston rod IQ is provided at its inner end with cross-head 89 to which is adjustably secured a follow-rod 00 that extends into receiver chamber 85 so that the valve I2, under actuation by transmitter 82. is caused to function as a follow-valve.

A drill spindle 9I disposed in the hollow piston rod I0 is rotatably supported at its inner end in ball bearing 92 and is fitted with a chuck 93 which may carry a tapping tool or, as shown in the drawing, a drill 94. At its other end drill spindle 9| has a spline connection with and is supported by a rotatable element of hydraulic motor 95, the said motor being mounted on a cross-head 96 which is in turn rigidly attached to the outer end of piston rod I0. 7

Control of the follow-valve I2 by the combined action of spring I8 and transmitter 32 is supplemented by mechanical stop means comprising a pin 97 rigidly connected to the valve, 9. plateshaped lever 98. supporting means for said lever, and adjustable stop rod 99 carried by cross-head 96. The plate 98 is retained in upright position by screws I60 and IOI which extend through vertically elongated slots in the plate and are attached to body 06. Sleeve I02 on screw IOI serves as a fulcrum abutment for the lower end of the plate. The plate is formed with laterally extending lugs 98a which rest upon supporting rods I03 carried by cross-head 96 and having slidin engagement at their front or inner ends with apertures in the main body 66. Rods I03 serve both to sustain the reaction of rotary motor 95 and to support plate 98. In normal operation of the apparatus plate 98 is sustained at the elevation shown in the drawings and when the motor piston is fed forward the stop rod 99 will engage the plate and cause it to contact pin 91 and move the valve 'I2 to its neutral or closed position tostop the advance of the drill.

In addition to the normal stop action last described above, provision is made for emergency Body 66 is bored to receive a tubular slide I04 which is held against rotation by pin I05. A spring I06 is arranged to resist rearward movement of the slide I04. Threaded rod I01 is adjustably mounted in slide ll 04 with its front end sli'dably supported in lug 8 Simon base 65. Near its outer end slide I04 is formed at its upper side with a notch I08 which is directly beneath the lower end of lever 98 when the tool is in the retracted position shown in the drawings. The plate-supporting rods I03, I03 also are formed on their top sides with notches I03a which, when the tool is retracted, are out of line with the plate 98, as shown in Fig. 2.

In the operation of the drill the front or inner end of the rod I0! is designed to operate as a probe in cooperation with a recess 63a formed in the face of the turret 63, the arrangement being such that the recess 63a is in accurate alignment with the rod I01 when the turret has been properly indexed to bring the work piece W into correct alignment with the drill. When the tool is in the retracted position shown in Fig. 2 the lower-end of cross-head 89 holds the slide I04 in the position shown with spring I06 under some tension. Hence when the tool moves forward from its retracted position the said spring causes rod I01 to move toward the turret. If the recess 63a of the turret is aligned with rod I0'I slide I04 will move forward far enough to carry its notch I08 out of alignment with the bottom of lever 98 and during the continued feeding movement of the tool the slide I04 will prevent the plate 93 from moving downward. If recess 63a is not in alignment with the probe I0! the latter will engage the face of the turret 33 and prevent more than a slight forward movement of slide I04. Then with continued forward movement of the motor piston, the supporting rods I03 will be advanced to brin their notches I03a under lugs 98a of the lever 98 thus interlocking the rods with the lever so that the upper end of the latter is moved forward to engage pin 91 and close valve 12. The feeding movement of the machine is thus stopped and engagement of the cutting tool with a wrong part of the work piece, or with the fixture in which the work piece is supported, is prevented.

To permit use of the rod I0'I for adjustment of the motor body 66 toward and away from the turret, a latch I09 is pivotally mounted on the rear end of base 65 in position to swing up into interlocking engagement with rod I07 so as to prevent the rod from endwise movement. With the motor piston retracted (valve I2 closed) and set screws 61 loosened, the body of the motor can then be adjusted forward or backward by rotating rod I01. Screws 61 are then tightened and latch I09 disengaged from rod I01.

The apparatus shown in Figs. 3 and 5 of the drawing presents an application of the present invention in which the combined motor control by the hydraulic transmitter and the automatic mechanical stop means is adapted to compensate for incorrect setting of the work piece in order to maintain uniformity of repetitive work performed, for example, the depth of a drilled hole.

In this lastapparatus the machine illustrated is of the same turret type as that shown in Figs. 2 and 4 and comprises top frame plate III, a

central block II2 sustaining turret II3, to which. is attached a fixture II4 to hold the work piece,

W As in the construction already described, the hydraulic motor comprises a body II5 adjustably mounted on base II6 which is bolted to the frame part III. The base II6 is fitted with a threaded rod II! which engages bod II5 to effect adjustment of the latter relative to turret II3.

The body H5 is formed with a cylinder bore 7 I I8 to-receive piston I I9 which is carried by tubu- 9 lar rod I29, th e pi s tongrod being provided at its front end with a erbss-heaa The body H5 is;: also boredi to receive,,follow valvesI22; which is biased toward the right by; spring 123,- and is fitted with a piston I24 which is exposed to pressure in receiviichanibrelfii 'Gdfidliit I23 con nectsthe receiver chamberwith a cam actuated transmittersirnilar to that'slioyvn in Fig; r351: low-rod l 'ifljcarried bypross'ehead fll en ceiver cham-br I25 The v. 7 1 ree eiii ii e f? ePeiaei ens ng.asihat eqwe. F he motor body I I5 is formed with passages to supply and exhaust working fluid to and from the motor cylinder under control of the valve in the same manner as in Figs. 2 and 4.

A drill spindle I29 rotatably mounted in piston rod I29 carries chuck I39 and drill I3I. A crosshead I32 is rigidly attached to the rear-end of piston rod I29 and in turn carries rotary hy draulic motor I33 which rotates spindle I 29. Cross-head pins I34 carried by cross-head I32 take the reaction of motor I33.

The mechanical control means to supplement the valve control by the hydraulic transmitter comprises a pin I35 which is rigidly attached to the follow-valve, a plate-shaped lever I33 which is loosely supported from body II5 by screw I3? and stop pin I38 adjustably mounted in crosshead I32. second plate-shaped lever I39 whichis formed with a vertical slot to receive a shouldered fulcrum screw I49 and the shouldered end of a stop rod I 4! which is slidably mounted in body H5 and supports lever I39. A cross-head I42 adjustably mounted on the threaded front end of stop rod I4I carries a torque rod I43 which slidably engages an aperture in the lower end of the cross-head I2I. A coil spring I44 is mounted on thestop rod between cross-heads I2| and I42,

The mechanism further comprises a the reaction of the spring being taken b pin I45 in rod MI. The cross-head I42 carries a contact plate I 43 designed to engage the work piece W In the operation of the last described apparatus, when the drill spindle I29 advances toward the work piece its movement is transmitted through spring I44 to the contact plate I46 and the latter is advanced with the spindle until its front end touches the work piece W as shown by dotted lines in Fig. 3. This advance of the stop rod I4! moves lever I39 to a vertical position indicated by dotted lines in Fig. 3 and permits the upper lever I39 also to move forward to its dotted line position. Thereafter, as the drill spindle continues to advance, spring I44 is compressed by reason of the engagement of contact plate I 43 with the work piece. Finally the stop pin I38 contacts the upper lever I36 and causes it to move the valve I22 to neutral or closed position, stopping the drill. The levers I35 and I39 are designed so that their arms, measured from their lower pivotal ends, are in the ratio of 1:2. Hence, in the operation just described, if the work piece W should be clamped in its fixture farther from the retracted position of the drill than it should be, there will be a correspondingly longer travel of the spindle before contact plate I46 engages the work and an exact- 1y similar increase in the travel of stop pin :33 before it engages lever I36 with the result that the hole drilled in the work will be of the true predetermined depth X. Similarly if the work is clamped too close to the retracted position of the drill, a less than normal forward feed of the drill spindle about contact of plate Elli with. h.

depth.

c 1,. parent that the present improvements-serve to notably x te'nd th use'fulfi'e f'bf thefapparatus disclosedinthe"applicatl serial Ne; 7=i9;3f )5 in fields-of panacea-an i quite high degree' of accuracy of serve-mete operationfifFur-th'eb r system; rfi'ak s' 'possible "the H o the apparatus to afiiygreatr stress '0 "hi nvolved' iiithe work ingstrgke of the fwlieras th"applicatioii of a positivast opd ectlyto the motor involves a stress equal to the maximum capacit of the motor. The latter practice calls for heavy ma chine parts and larger costs both direct and incidental.

It will be apparent from the nature of the ex emplary embodiments of the invention herein disclosed that the invention is applicable in a wide variety of structural forms and for many diiferent purposes. The appended claims are intended to be read, accordingly, as covering a wide range of embodiments within their bounds.

What is claimed is:

1. The combination of a hydraulic servo-motor having a follow-valve; means for supplying pressure fluid to the motor under control of its follow-valve; and means for actuating the followvalve comprising a hydraulic transmitter, mechanical means for operating the transmitter, a hydraulic receiver having a piston arranged to move the follow-valve, conduit means and a body of liquid therein operatively interposed between the transmitter and the receiver to transfer transmitter movement to the receiver and its piston and thereby apply moving force to the follow-valve, an element of the means for applying the said moving force to the valve being constructed to yield under predetermined stress, and unyielding mechanical means arranged for engagement with the valve structure and operable when so engaged to apply to the valve a moving force induced by movement of one of the two power elements of the motor in opposition to the force of the hydraulic transmitter.

2. Hydraulic apparatus as claimed in claim 1 in which the follow-valve motor has its piston element fixed against axial movement and its cylinder element supported for such movement.

3. Hydraulic apparatus as claimed in claim 2, in which the unyielding mechanical means for applying moving force to the follow-valve comprises a template arranged for relatively movable engagement with the follow-valve structure and in which the cylinder element of the follow-valve motor is mounted for movement transversely of the motor axis to provide lateral movement of the follow-valve structure relative to the template while the former is maintained in contact with the latter by the pressure of the hydraulic transmitter.

4. Hydraulic apparatus as claimed in claim 1 in which the mechanical means for actuating the hydraulic transmitter comprises a motordriven cam, in which the train of pressure-transmitting means between such cam and the followvalve comprises a movable means constructed to yield under a force somewhat in excess of that required to overcome the resistance to movement of the follow-valve, and in which the cam is icehhd stdp pin l as minawe at ia'oIre'spDIidIngI-y aveirofzu e spinaie, and

'1 sens -meter 11 shaped to establish such a force when the follow-valve structure is in operative engagement with its unyielding mechanical actuating means and to establish a corresponding force between the follow-valve structure and said unyielding mechanical actuating means.

5. Hydraulic apparatus as claimed in claim 1 in which the mechanical means for actuating the hydraulic transmitter comprises a motordriven cam, and in which the train of pressuretransmitting means between such cam and the follow-valve comprises a movable means constructed to yield under a force somewhat in excess of that required to overcome the resistance to movement of the follow-valve.

EDWARD M. MAY.

,, a, 12 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 752,491 Warner Feb. 16, 1904 1,957,759 Coates May 8, 1934 1,965,867 Vickers July 10, 1934 2,154,718 Bannon Apr. 18, 1939 2,236,467 Clench Mar. 25, 1941 

